3 seismology and earth structure - snuseismo.snu.ac.kr/class/seismology/swch3.2-3.3.pdf · 3...
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3 Seismology and Earth Structure
• Determine Velocity structure– Travel time, Dispersion, Eigen frequencies …
• Refraction Seismology• Reflection Seismology• Seismic Waves in a spherical earth• Body wave travel time studies• Anisotropic earth structure• Attenuation and anelasticity• Composition of mantle and core
3.2 Refraction Seismology
• Flat layer method• Dipping layer method• Advanced analysis methods• Crustal structure• Rocks and minerals
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Portable Seismometers
Data acquisition Parameters
Number of seismic stations
Distance between stations Average 1.5 km
170 Vertical-Component 28 Three-Component Total 198 Stations
Sampling rate 120 Hz
Record length 120 sec
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Record section of shot at Seosan
(2-15hz Bandpass filtered)
Record section of shot at Yeongdong
(2-15hz Bandpass filtered)
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Ray trajectory and corresponding synthetics (Seosan)
Ray trajectory and corresponding synthetics (Yeongdong)
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Final layered velocity model
Geology and tectonic provinces of the southern Korean Peninsula
Gyeonggi massifGyeonggi massif
Gyeongsang
Okcheonfold belt
Yeongnammassif
Gyeongsangbasin
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002 sin)/(sin iTvviTvx jjjjjj Δ=Δ=
∑
∑=
Δ
+=Δ==
n
nn
n
jjj
TTVxdT
tVxxTTvxv
idxdT
22
2222
0
2
0
0
/)2(
/)(,)2/(sin
∑∑
∑
==
=
ΔΔ=
Δ=⇒=
n
jj
n
jjjn
jjjn
n
tTvV
TTvVTVdx
00
22
0
222
)/()(
/)2(
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3.3.7 Migration
Migration tries to find surfaces in the case of non-horizontal layers –to remove the effects of point diffractors
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Bright spot:
A strong reflectionat the interface between
a gas layer andunderlying oil or water
in hydrocarbon reservoir
Horizontal or “flat spot”
Detection depends onppull-up or pull-down effects caused by variability in
the thickness or velocity of layers above.